How did iridium and tektites provide evidence of an impact at the end of the Cretaceous?

The discovery of iridium and tektites at the Cretaceous–Paleogene (K–T) boundary provides critical evidence for a massive asteroid impact approximately 66 million years ago.123

• Iridium Anomaly: Iridium is a rare metal on Earth’s surface but is found in high concentrations in meteorites and the Earth's mantle. In the 1970s, researchers identified a worldwide layer of clay at the K–T boundary containing an "iridium spike" significantly higher than background levels. This global distribution suggests that a massive extraterrestrial object—estimated at 10–15 km in diameter—collided with Earth, dispersing debris across the planet.143
• Tektites: These are natural glass objects formed by the intense heat and pressure of meteorite impacts. Tektites found in K–T boundary deposits, such as those in Haiti and Mexico, share the same age and isotopic composition as the Chicxulub crater. Their presence confirms a high-energy collision that ejected molten rock into the atmosphere, which then cooled into glass as it fell back to Earth.32

Together, these markers support the theory that the impact triggered catastrophic environmental changes, including global darkness and climate shifts, leading to the mass extinction of the dinosaurs.143